1. Field of the Invention
This invention relates to golf clubs of the iron type and, in particular, to a method of manufacture of of a golf iron having an improved weight distribution.
2. Description of the Prior Art
Golf irons are commonly manufactured as solid metal castings having the approximate weight and the shape desired for the numbered catagory of the iron. The irons are commonly grouped into numbered catagories from one to nine with the lowest numbered iron having the longest shaft, the flattest or most vertical face and the lightest head weight. As the catagory number increases, the face becomes more inclined from the vertical, the shaft shortens about one-half inch and the weight of the club head increases by about 7 grams for each number change. Golf irons also include specialty irons such as a sandwedge and the like which have a striking face which is generally at a greater angle from the vertical than even the highest numbered iron.
Golf irons are also manufactured with varied moment arms about a point 12 inches from the upper end of the club shaft. These moment arms, commonly referred to as swing weights are grouped in classes designated from C to F and in numbered series from one to 10 within each class. This variation in the swing weight of the clubs is desirable to permit each player to select precisely the set of the clubs having the best swing weight for his size, strength and golfing skill.
In the conventional manufacture, the heads of the irons are formed as a solid body with a neck and dependent hozel for insertion of the club shaft. The desired swing weight is obtained by loading a predetermined amount of weights in the bottom of the shaft.
The aforementioned manufacture does not achieve optimum weight distribution in a golf iron head. Because the head is a unitary, solid casting, the upper portion of the head cannot be lightened sufficiently to obtain as low a center of gravity as is desirable to attain maximum loft in the trajectory of a ball struck by the iron. Additionally, weighting the individual irons by loading weights in the shaft to achieve the desired weight locates material in the shaft above the club head. This not only damages the dynamic characteristics of the shaft but the additional weight above the heel of the club head raises the center of gravity of the striking portion of the club and moves it towards the heel of the head, tending to induce a slice.
There has recently been developed a golf iron construction in which the weight distribution of the head is controlled to lower the center of gravity and to insure symmetry about the impact center. This method comprises casting, by the investment process, metal to form a head body which has an internal cavity that extends from the top edge of the head, beneath substantially the entire face of the head. The cavity, which is formed by use of a ceramic insert in the mold, is filled with a low density material such as an epoxy resin and predetermined amounts of weights such as lead shot and the like, are placed in the bottom of the cavity to maintain a low center of gravity and symmetrical weight distribution.
Unfortunately, the manufacturing tolerances in casting of an iron head body with a thin face and subjacent cavity do not permit a high yield of acceptable products. Commonly, the face must be cast with a thickness of approximately 0.05 inch with longitudinal grooves, to enhance the frictional contact with the ball, scored along its exterior surface to a depth of approximately 0.015 to 0.03 inch. The experience with manufacturing iron heads of this type is that approximately 80% of the products are not acceptable because of warping of the thin, grooved face of the head. Accordingly, this manufacturing method does not provide a simple and inexpensive manufacture of the iron head of improved construction.